1. Field of the Invention
The present invention relates to an image deformation processing device and an image deformation processing method for carrying out the deformation process for an image, such as the fine variable magnification, the shift process or the like.
2. Description of Related Art
In an image output apparatus or the like using the electrophotographic process, the positional displacement, such as the fine displacement of the image position or the magnification between the front surface and the back surface of the recording paper, the image positional displacement between the colors (misregistration) and the like, is caused by the fixing irregularity and irregularity in the paper conveyance. In order to correct the above positional displacement, the deformation process for deforming an image in two-dimension, such as the shift, the rotation, the enlargement/reduction of an image and the like, is carried out.
As the deformation process, the enlargement/reduction process for the image is realized by inserting or deleting pixels. For example, in case that an image having a dot matrix form in which the pixels are arranged in a grid form extending in two directions which are perpendicular to each other (one direction is referred to as the main scanning direction (the horizontal direction or the line direction) and the other direction is referred to as the sub-scanning direction (or the vertical direction)) is enlarged in the sub-scanning direction, in a simple nearest neighbor algorithm, as shown in FIG. 23B, pixels are concurrently inserted in the identical line (in the main scanning direction) in each interpolation period. FIGS. 23A to 23C show an example in which the original image shown in FIG. 23A is enlarged in the sub-scanning direction by 8/7 times. In FIG. 23B, pixels constituting one line are inserted at intervals of 7 lines.
When the variable magnification is carried out in the above method, because the pixel insertion positions are arranged on the identical line, the texture is caused by a certain type of regularity in the image. For example, when the original image in which the stripes are drawn as shown in FIG. 24A is variably magnified in the pixel insertion method shown in FIG. 23B, the stripes become bold periodically as shown in FIG. 24B. As a result, the image quality is deteriorated.
Therefore, as shown in FIG. 23C, a method in which the pixel insertion/deletion positions in the image are dispersed is adopted. It is considered that the above method is the most preferable for the image quality in the electrophotographic process. FIG. 24C shows the image obtained by variably magnifying the original image shown in FIG. 24A by using the method in which the pixel insertion positions are dispersed as shown in FIG. 23C (pixel insertion dispersing process). As the concrete method for dispersing the pixel insertion positions, for example, the following method is disclosed in Japanese Patent Application Publication No. 2006-270149. In the method, the pattern for dispersing the pixel insertion positions or the pixel deletion positions is defined in the matrix having N pixels×M pixels, and the pixel insertion positions or the pixel deletion positions are determined in the whole of image data by repeatedly applying the above matrix.
On the other hand, also in case that the image is shifted in the rotation process, the skew/bow correction process or the like for the image, it is known that the method for dispersing the shift amount stochastically in the horizontal direction is preferable in the electrophotographic process. For example, when the simple skew/bow correction process (simple process) is carried out for the original image in which the stripes are drawn as shown in FIG. 25A, the steps caused at the specific positions in the main scanning direction in the stripes as shown in FIG. 25B are conspicuous. However, when the shift dispersion process for dispersing the shift amount stochastically in the horizontal direction is carried out, the image shown in FIG. 25C is obtained. In case that the image is printed in the electrophotographic process, the steps become inconspicuous.
In the deformation process for adjusting the positions of the images to be printed on the front surface and the back surface of the recording paper, it is necessary to form the final image in view of a plurality of correction elements (the rotation, the enlargement/reduction, the skew correction, the bow correction and the like). In this case, for example, when the skew correction process is separately carried out by using the shift dispersion process for dispersing the shift amount stochastically in the horizontal direction after the enlargement process is carried out by dispersing the pixel insertion positions (or the pixel deletion positions), the steps having the difference of two pixels are caused. As a result, there is a problem in which the image quality is significantly deteriorated. FIG. 26A shows the original image in which the stripes are drawn. FIG. 26B shows the image obtained by carrying out the pixel insertion dispersing process in which the original image is enlarged by dispersing the pixel insertion positions. FIG. 26C shows the image obtained by carrying the shift dispersion process for dispersing the shift amount stochastically in the horizontal direction, for the image shown in FIG. 26B. In the portion enclosed by the circle 101 shown in FIG. 26C, the step having the difference of two pixels is caused, and the image quality is deteriorated.